The present invention relates generally to electronic ballasts and associated methods for powering lighting sources such as fluorescent lamps. More particularly, the present invention relates to an electronic ballast having circuitry for detecting the presence or removal of one or more common lamp filaments and regulating the performance of an associated output stage accordingly.
Dimming ballasts are generally desirable for, among other things, light output control and associated energy savings. If a conventional dimming ballast has a parallel connection of common lamp filaments it is very difficult to sense removal of one of the common filaments by using DC current or voltage sensing procedures as are currently known in the art. This is a primary reason why most dimming ballasts do not shut down when a common filament is removed from the ballast, meaning that there is a distinct possibility for a technician to get shocked by open circuit voltage when re-lamping. If the open circuit voltage is sufficiently high, the ballast may fail safety tests for issues such as through-lamp leakage.